## Installation and Startup ### Installing Arthas ```bash # Method 1: Using official script (recommended) curl -O https://arthas.aliyun.com/arthas-boot.jar # Method 2: Install via package manager # CentOS/RHEL yum install -y arthas # Ubuntu/Debian apt install -y arthas ``` ### `java -jar arthas-boot.jar` - Start Arthas - `--target-ip `: Specify target server IP for remote diagnosis. - `--telnet-port `: Specify telnet port, default 3658. - `--http-port `: Specify HTTP port, default 8563. - `--session-timeout `: Set session timeout, default 1800 seconds. - `--select `: Directly select specified Java process, skip interactive selection. ### Connecting to Target Process After startup, all Java processes will be listed. Enter the corresponding number to select and connect to the target process. ## Basic Operation Commands ### `help` - View Help Information - `help `: View detailed help for a specific command. - `help`: Show list of all available commands. ### `version` - View Arthas Version Information Display current Arthas version, Java version and other information. ### `history` - View Command History Display command history executed in current session. ### `quit` / `exit` - Exit Arthas - `quit`: Exit current Arthas client without affecting other connections. - `stop`: Completely stop Arthas server. ### `cls` - Clear Screen Clear current terminal screen content. ## JVM Information Monitoring ### `dashboard` - Real-time Data Panel - `-i `: Set refresh interval, default 5 seconds. - `-n `: Specify refresh count, default unlimited. - **Display Content**: CPU usage, memory usage, GC status, thread information, etc. ### `jvm` - View JVM Information Display detailed JVM information including system properties, memory usage, class loaders, compiler, etc. ### `sysprop` - View and Modify System Properties - `sysprop`: Display all system properties. - `sysprop `: View specified system property. - `sysprop `: Modify specified system property. ### `sysenv` - View System Environment Variables - `sysenv`: Display all environment variables. - `sysenv `: View specified environment variable. ### `memory` - View JVM Memory Information - `memory`: Display detailed usage of heap memory, non-heap memory, direct memory, etc. ### `perfcounter` - View Performance Counters Display JVM internal performance counter information for performance analysis. ## Thread Analysis ### `thread` - View Thread Information - `thread`: Display all thread information, sorted by CPU usage. - `thread `: Display detailed information and stack trace of specified thread. - `thread -n `: Display top N busiest threads. - `thread -b`: Display threads in BLOCKED state. - `thread --state `: Display threads in specified state (RUNNABLE, BLOCKED, WAITING, etc.). - `thread -i -n `: Collect thread CPU usage statistics at specified intervals. ### `jstack` - Generate Thread Dump - `jstack`: Similar to `jstack` command but executed within Arthas environment. ## Class Loading Analysis ### `classloader` - View Class Loader Information - `classloader`: Display statistics of all class loaders. - `classloader -l`: Display class loader hierarchy. - `classloader -c `: Display classes loaded by specified class loader. - `classloader -r `: Search for resources in class loaders. ### `sc` - Search Class Information - `sc `: Search for matching classes. - `sc -d `: Display detailed class information (fields, methods, etc.). - `sc -f `: Display class field information. - `sc -x `: Specify expand level for class information display. - **Wildcard Support**: Supports `*` and `?` wildcards. ### `sm` - Search Method Information - `sm `: Search for methods in class. - `sm -d `: Display detailed method information. - `sm -Ed `: Display detailed method information with expanded parameter types. ### `jad` - Decompile Class - `jad `: Decompile specified class. - `jad `: Decompile specific method of specified class. - `jad --source-only `: Only show source code without class loader information. - `jad -c `: Decompile from specified class loader. ## Method Monitoring and Tracing ### `monitor` - Method Execution Monitoring - `monitor `: Monitor method call statistics. - `monitor -c `: Specify statistics cycle (default 120 seconds). - `monitor -E `: Enable regex pattern matching. - **Statistics**: Call count, success count, failure count, average time, failure rate, etc. ### `watch` - Method Execution Observation - `watch `: Observe method parameters, return values, exceptions. - `watch '{params, returnObj}' -x 2`: Observe parameters and return values, expand 2 levels. - `watch '{params[0], returnObj}' '#cost > 100'`: Only observe calls taking more than 100ms. - `-x `: Specify object expand level. - `-n `: Specify observation count. - `-b`: Observe before method call. - `-e`: Observe when method throws exception. - `-s`: Observe after method returns. - `-f`: Observe after method call finishes (including exceptions). ### `trace` - Method Call Path Tracing - `trace `: Trace internal call path and time cost of method. - `trace '#cost > 10'`: Only trace calls taking more than 10ms. - `trace -E `: Use regex pattern matching. - `trace --skipJDKMethod false `: Include JDK method tracing. ### `stack` - Method Call Stack - `stack `: Display call stack path of method invocation. - `stack '#cost > 5'`: Only show call stacks taking more than 5ms. - `stack -n 1 `: Only capture one call stack. ### `tt` - Time Tunnel - `tt -t `: Record method call information. - `tt -l`: Display all records in time tunnel. - `tt -s ''`: Search records. - `tt -i `: View details of record at specified index. - `tt -p `: Re-execute method call at specified index. - `tt --delete-all`: Delete all records. ## Performance Analysis ### `profiler` - Performance Profiler (Requires JDK 8u40+) - `profiler start`: Start CPU performance profiling. - `profiler start --event cpu`: Specify CPU event analysis. - `profiler start --event alloc`: Analyze memory allocation. - `profiler stop`: Stop profiling and generate report. - `profiler status`: View profiler status. - `profiler stop --format html`: Generate HTML format report. - `profiler list`: Display all supported event types. ### `heapdump` - Generate Heap Dump - `heapdump`: Generate heap dump file to default location. - `heapdump /tmp/dump.hprof`: Generate heap dump to specified file. - `heapdump --live`: Only dump live objects. ### `vmtool` - JVM Tools - `vmtool --action getInstances --className `: Get all instances of specified class. - `vmtool --action getInstances --className --limit 10`: Limit number of returned instances. - `vmtool --action forceGc`: Force garbage collection. ## Bytecode Operations ### `mc` - Memory Compiler - `mc `: Compile Java source file. - `mc -c `: Compile with specified class loader. - `mc -d `: Specify output directory. ### `retransform` - Class Retransformation - `retransform `: Retransform loaded class. - `retransform -c `: Retransform with specified class loader. - `retransform -l`: Display all retransformed classes. - `retransform --deleteAll`: Delete all retransformed classes and restore original state. ### `redefine` - Class Redefinition - `redefine `: Redefine loaded class. - `redefine -c `: Redefine with specified class loader. - **Note**: Difference between `redefine` and `retransform` lies in scope and recovery mechanism. ### `dump` - Dump Class - `dump `: Dump bytecode of specified class to default directory. - `dump -d `: Dump to specified directory. - `dump -c `: Dump from specified class loader. ## Hot Reloading Practice ### Typical Hot Reloading Workflow 1. **Save Original Class**: `dump com.example.MyClass` 2. **Compile New Code**: `mc /path/to/MyClass.java` 3. **Reload Class**: `retransform /path/to/MyClass.class` 4. **Verify Update**: Verify new logic through `watch` or `trace` 5. **Restore Original**: `retransform --deleteAll` (if rollback needed) ### Considerations - Hot reloading has limitations: cannot add/remove fields and methods, cannot modify method signatures - Recommend testing hot reloading effects in test environment first - Important changes should go through normal release process, hot reloading is mainly for emergency fixes ## Web Console ### Starting Web Console When Arthas starts, Web console is automatically enabled on default port 8563. ### Access Methods - **Local Access**: `http://localhost:8563` - **Remote Access**: `http://:8563` ### Web Console Features - Execute all Arthas commands - Real-time Dashboard viewing - File upload and download - Session management ## Advanced Techniques ### OGNL Expressions Arthas supports OGNL (Object-Graph Navigation Language) expressions: - `@ClassName@staticMethod()`: Call static method - `#field`: Access Spring environment variables - `target.field`: Access object field - `params[0].field`: Access parameter field ### Conditional Expressions Use conditions in `watch`, `trace`, `monitor` and other commands: - `'#cost > 100'`: Time cost more than 100ms - `'params[0] != null'`: First parameter is not null - `'returnObj.status == 200'`: Return object status is 200 ### Batch Operations - Batch monitoring with wildcards: `watch com.example.service.* * '{params, returnObj}'` - Using regex: `trace -E com\.example\..*Service .*Method` ### Script Execution - Save commonly used Arthas commands as script files - Execute via `as.sh` script: `./as.sh --batch-file commands.txt` ## Troubleshooting Scenarios ### High CPU Usage ```bash # 1. Check overall situation dashboard # 2. Find threads with highest CPU usage thread -n 5 # 3. Analyze specific thread thread # 4. If business thread, trace hotspot methods profiler start # Wait for some time profiler stop --format html ``` ### Memory Leak Investigation ```bash # 1. Check memory usage memory # 2. Check heap usage details dashboard # 3. Generate heap dump file heapdump /tmp/heap.hprof # 4. View instances of a class vmtool --action getInstances --className java.lang.String --limit 10 ``` ### Slow API Response ```bash # 1. Monitor method execution statistics monitor com.example.controller.UserController getUserInfo # 2. Trace method call chain trace com.example.controller.UserController getUserInfo # 3. Observe method parameters and return values watch com.example.controller.UserController getUserInfo '{params, returnObj, #cost}' -x 2 # 4. Filter slow requests with conditions watch com.example.controller.UserController getUserInfo '{params, returnObj, #cost}' '#cost > 1000' ``` ### Deadlock Detection ```bash # View all threads in BLOCKED state thread -b # View detailed thread information thread # Generate thread dump jstack ``` ### Class Loading Issues ```bash # Search for classes sc *UserService* # View class details sc -d com.example.service.UserService # View class loaders classloader # Check class conflicts sc -d com.example.service.UserService | grep classLoaderHash ``` ## Security Considerations ### Production Environment Usage Recommendations - **Access Control**: Only allow operations personnel to access Arthas ports - **Session Management**: Close unnecessary sessions promptly - **Performance Impact**: Avoid complex tracing operations during peak hours - **Data Sensitivity**: Be aware that `watch` command may leak sensitive data ### Permission Control - Restrict Arthas port access through firewall - Consider using TLS encryption for Web console connections - Regularly audit Arthas usage logs ### Exit Cleanup - Execute `stop` command promptly after use - Clean up generated temporary files (dump files, analysis reports, etc.) - Restore all hot-reloaded classes: `retransform --deleteAll`

Arthas Java Diagnostic Tool Operations Guide